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  <title>播下一个更好的随机数发生器种子</title>

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</div><hr /><div id="function.mt-srand" class="refentry">
   <div class="refnamediv">
    <h1 class="refname">mt_srand</h1>
    <p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">mt_srand</span> &mdash; <span class="dc-title">播下一个更好的随机数发生器种子</span></p>

   </div>
 <div class="refsect1 description" id="refsect1-function.mt-srand-description">
  <h3 class="title">说明</h3>
   <div class="methodsynopsis dc-description">
    <span class="type"><span class="type void">void</span></span> <span class="methodname"><strong>mt_srand</strong></span>
     ([ <span class="methodparam"><span class="type">int</span> <code class="parameter">$seed</code></span>
   ] )</div>

    <p class="para rdfs-comment">
     用
     <em><code class="parameter">seed</code></em> 来给随机数发生器播种。 没有设定 <em><code class="parameter">seed</code></em> 参数时，会被设为随时数。
    </p>

    <blockquote class="note"><p><strong class="note">Note</strong>: <span class="simpara">自 PHP 4.2.0 起，不再需要用
<span class="function"><a href="function.srand.html" class="function">srand()</a></span> 或 <span class="function"><strong>mt_srand()</strong></span>
给随机数发生器播种 ，因为现在是由系统自动完成的。</span></p></blockquote>
  
   </div>

 <div class="refsect1 parameters" id="refsect1-function.mt-srand-parameters">
  <h3 class="title">参数</h3>
  <p class="para">
   <dl>

    
     <dt>
<em><code class="parameter">seed</code></em></dt>

     <dd>

      <p class="para">
       可选的种子值
      </p>
     </dd>

    
   </dl>

  </p>
 </div>


 <div class="refsect1 returnvalues" id="refsect1-function.mt-srand-returnvalues">
  <h3 class="title">返回值</h3>
  <p class="para">
   没有返回值。
  </p>
 </div>


 <div class="refsect1 changelog" id="refsect1-function.mt-srand-changelog">
  <h3 class="title">更新日志</h3>
  <p class="para">
   <table class="doctable informaltable">
    
     <thead>
      <tr>
       <th>版本</th>
       <th>说明</th>
      </tr>

     </thead>

     <tbody class="tbody">
      <tr>
       <td>4.2.0</td>
       <td>
        The <em><code class="parameter">seed</code></em> becomes optional 
        and defaults to a random value if omitted.
       </td>
      </tr>

      <tr>
       <td>5.2.1</td>
       <td>
        The Mersenne Twister implementation in PHP now uses a new seeding
        algorithm by Richard Wagner. Identical seeds no longer produce the same
        sequence of values they did in previous versions. This behavior is not
        expected to change again, but it is considered unsafe to rely upon it
        nonetheless.
       </td>
      </tr>

     </tbody>
    
   </table>

  </p>
 </div>

 <div class="refsect1 examples" id="refsect1-function.mt-srand-examples">
  <h3 class="title">范例</h3>
  <p class="para">
   <div class="example" id="example-3376">
    <p><strong>Example #1 <span class="function"><strong>mt_srand()</strong></span> 例子</strong></p>
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #FF8000">//&nbsp;seed&nbsp;with&nbsp;microseconds<br /></span><span style="color: #007700">function&nbsp;</span><span style="color: #0000BB">make_seed</span><span style="color: #007700">()<br />{<br />&nbsp;&nbsp;list(</span><span style="color: #0000BB">$usec</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$sec</span><span style="color: #007700">)&nbsp;=&nbsp;</span><span style="color: #0000BB">explode</span><span style="color: #007700">(</span><span style="color: #DD0000">'&nbsp;'</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">microtime</span><span style="color: #007700">());<br />&nbsp;&nbsp;return&nbsp;(float)&nbsp;</span><span style="color: #0000BB">$sec&nbsp;</span><span style="color: #007700">+&nbsp;((float)&nbsp;</span><span style="color: #0000BB">$usec&nbsp;</span><span style="color: #007700">*&nbsp;</span><span style="color: #0000BB">100000</span><span style="color: #007700">);<br />}<br /></span><span style="color: #0000BB">mt_srand</span><span style="color: #007700">(</span><span style="color: #0000BB">make_seed</span><span style="color: #007700">());<br /></span><span style="color: #0000BB">$randval&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">mt_rand</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>
  </p>
 </div>

 <div class="refsect1 seealso" id="refsect1-function.mt-srand-seealso">
  <h3 class="title">参见</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member"><span class="function"><a href="function.mt-rand.html" class="function" rel="rdfs-seeAlso">mt_rand()</a> - 生成更好的随机数</span></li>
    <li class="member"><span class="function"><a href="function.mt-getrandmax.html" class="function" rel="rdfs-seeAlso">mt_getrandmax()</a> - 显示随机数的最大可能值</span></li>
    <li class="member"><span class="function"><a href="function.srand.html" class="function" rel="rdfs-seeAlso">srand()</a> - 播下随机数发生器种子</span></li>
   </ul>
  </p>
 </div>

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